Certain antimony compounds are known to be used to treat those cracking catalysts conventionally employed in the catalytic cracking of hydrocarbons for the production of gasoline, motor fuel, blending components and light distillates. These conventional cracking catalysts generally contain silica, or silica-alumina. Such materials are frequently associated with zeolitic materials. These zeolitic materials can be naturally occurring, or they can be produced by conventional ion exchange methods such as to provide metallic ions which improve the activity of the catalyst.
While the presence of certain metals can be beneficial, the presence of others in the catalyst is detrimental. It is well known that verying amounts of metals such as nickel, vanadium and iron cause deterioration of the cracking catalyst during the cracking process. In fact, some oils contain these metals in such a high concentration that they cannot be economically cracked into gasoline and other fuels. The metals accumulate on the cracking catalyst and cause increased hydrogen production and coke laydown on the cracking catalyst, thereby adversely affecting the yield of desired products.
It has heretofore been proposed that those deleterious metals can be passivated by treating the contaminated catalyst with compounds containing antimony, tin, indium or bismuth (see U.S. Pat. No. 4,257,919). Antimony compounds are particularly useful as passivating agents and use of a wide variety of both organic and inorganic antimony compounds have been proposed for that purpose (see U.S. Pat. Nos. 4,111,845 and 4,153,536). Among the organic antimony compounds proposed are antimony tricarboxylates such as antimony tridodecanoate and antimony trioctadecanoate.
Prior art processes for antimony tricarboxylate preparation involve a direct reaction between antimony oxide and a carboxylic acid anhydride. Nerdel et al (J.Chem.Ber., 90, 598 (1957)) teach that antimony triacetate or antimony tribenzoate can be prepared by reacting antimony oxide with acetic anhydride or benzoic anhydride, respectively.
Ventura et al (U.S. Pat. No. 3,803,193) disclose reacting antimony tricarboxylates with alcohols to produce antimony trialkoxides. Ventura indicates that the tricarboxylate can be prepared by reacting antimony oxide with an organic acid anhydride directly or in some instances with an acid directly. The acid by-product of the tricarboxylate-alcohol reaction is taught to be neutralized with ammonia and removed as ammonium acetate solid.
The direct production of antimony tricarboxylates by the prior art methods of direct reaction between antimony oxide and the desired acid anhydride is not satisfactory for producing higher tricarboxylates because the higher anhydrides are not readily available and are synthetically prepared only with great difficulty. Accordingly, it is an object of the present invention to provide a process for preparation of higher tricarboxylates of antimony which uses readily available reactants and affords high yields of the desired tricarboxylates. It is another object of the invention to provide a synthetic method of preparation wherein the antimony tricarboxylate produced is substantially free of deletrious impurities without extensive purification and has a high level of thermal stability. These and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from the following description of the invention.